P0340 Fault on 2005 Pontiac Sunfire: No Cam Position Sensor? Engine Replacement Needed?
I'm back with a follow-up on my 2005 Pontiac Sunfire. A mechanic recently performed a timing chain re-alignment during a teardown, as the marks were misaligned when the timing cover was removed. After realigning the components and ensuring the chain is properly tensioned, no visible damage was found. Compression testing (dry) revealed two cylinders with significantly low readings—though I don't have exact numbers. The mechanic suggested it could be due to worn piston rings or internal engine issues, leading me to consider replacing the entire engine as a potential solution. Given my car's history and current symptoms, what would you diagnose? Is there any way to confirm engine failure without full disassembly? Additional details: I did not perform a wet compression test. There is fuel in the oil, which was attributed to repeated attempts to start the vehicle. The car does not currently start—timing cover and valve covers are still off after re-alignment. The chain, guides, and components were inspected and appear intact post-realignment. I'm hoping there's a way to diagnose the issue without replacing the engine entirely.
Why was cam timing realigned? What was the original cause, and what corrective action was taken? Low compression is concerning—but which cylinders are affected? Are you certain it's engine failure? There are diagnostic tests to identify compression leaks—such as a compressed air leak test. Inject compressed air into each cylinder; if it escapes past rings or valves, that indicates internal wear. Also, note: the car doesn't start. Does it run at all when properly assembled? What about fuel in oil—was this present before or after attempts to start?